共查询到20条相似文献，搜索用时 31 毫秒
1.
The semiconducting properties of a wide range of minerals are often ignored in the study of their interfacial geochemical behavior. We show that surface-specific charge density accumulation reactions combined with bulk charge carrier diffusivity create conditions under which interfacial electron transfer reactions at one surface couple with those at another via current flow through the crystal bulk. Specifically, we observed that a chemically induced surface potential gradient across hematite (alpha-Fe2O3) crystals is sufficiently high and the bulk electrical resistivity sufficiently low that dissolution of edge surfaces is linked to simultaneous growth of the crystallographically distinct (001) basal plane. The apparent importance of bulk crystal conduction is likely to be generalizable to a host of naturally abundant semiconducting minerals playing varied key roles in soils, sediments, and the atmosphere. 相似文献
2.
Sikes HD Smalley JF Dudek SP Cook AR Newton MD Chidsey CE Feldberg SW 《Science (New York, N.Y.)》2001,291(5508):1519-1523
We measured rate constants of thermal, interfacial electron transfer through oligophenylenevinylene bridges between a gold electrode and a tethered redox species in contact with an aqueous electrolyte using the indirect laser-induced temperature jump technique. Analysis of the distance dependence indicates that, unlike other bridges studied to date, the rate constants are not limited by electronic coupling for bridges up to 28 angstroms long. The energy levels of the bridges relative to those of the redox species rule out hopping through the bridge. We conclude that, out to 28 angstroms, the transfer is limited by structural reorganization and that electron tunneling occurs in less than 20 picoseconds, suggesting that oligophenylenevinylene bridges could be useful for wiring molecular electronic elements. 相似文献
3.
以熟红黄泥为试验材料，研究了在淹水培养过程中不同氧化还原条件下外加Se(Ⅵ）在土壤溶液中的价态转化。结果表明，在两种土壤Eh培养条件下，外加的Se(Ⅵ）约有20％进入土壤固化，80％进入土壤溶液。在低Eh值（175mV )条件下，进入土壤溶液的硒约有90％呈有机态，且较稳定；10％左右的Se(Ⅵ）还原为Se(Ⅳ），此还原以应符合动力学一级方程，半衰期为3．7d。 在高Eh值（450mV）条件下，进入土壤溶液的硒在第一天70．9％呈Se(Ⅵ）态，且稳定；29．0呈有机态，并在培养过程中先氧化成Se(Ⅵ），然后Se(Ⅳ）再氧化成Se(Ⅵ）。 相似文献
4.
Fuhrer MS Nygard J Shih L Forero M Yoon YG Mazzoni MS Choi HJ Ihm J Louie SG Zettl A McEuen PL 《Science (New York, N.Y.)》2000,288(5465):494-497
Junctions consisting of two crossed single-walled carbon nanotubes were fabricated with electrical contacts at each end of each nanotube. The individual nanotubes were identified as metallic (M) or semiconducting (S), based on their two-terminal conductances; MM, MS, and SS four-terminal devices were studied. The MM and SS junctions had high conductances, on the order of 0.1 e(2)/h (where e is the electron charge and h is Planck's constant). For an MS junction, the semiconducting nanotube was depleted at the junction by the metallic nanotube, forming a rectifying Schottky barrier. We used two- and three-terminal experiments to fully characterize this junction. 相似文献
5.
One-dimensionally connected organic nanostructures with dissimilar semiconducting properties are expected to provide a reliable platform in understanding the behaviors of photocarriers, which are important for the development of efficient photon-to-electrical energy conversion systems. Although bottom-up supramolecular approaches are considered promising for the realization of such nanoscale heterojunctions, the dynamic nature of molecular assembly is problematic. We report a semiconducting nanoscale organic heterojunction, demonstrated by stepwise nanotubular coassembly of two strategically designed molecular graphenes. The dissimilar nanotubular segments, thus connected noncovalently, were electronically communicable with one another over the heterojunction interface and displayed characteristic excitation energy transfer and charge transport properties not present in a mixture of the corresponding homotropically assembled nanotubes. 相似文献
6.
Piezoelectric nanogenerators based on zinc oxide nanowire arrays 总被引：2，自引：0，他引：2
We have converted nanoscale mechanical energy into electrical energy by means of piezoelectric zinc oxide nanowire (NW) arrays. The aligned NWs are deflected with a conductive atomic force microscope tip in contact mode. The coupling of piezoelectric and semiconducting properties in zinc oxide creates a strain field and charge separation across the NW as a result of its bending. The rectifying characteristic of the Schottky barrier formed between the metal tip and the NW leads to electrical current generation. The efficiency of the NW-based piezoelectric power generator is estimated to be 17 to 30%. This approach has the potential of converting mechanical, vibrational, and/or hydraulic energy into electricity for powering nanodevices. 相似文献
7.
Bell LE 《Science (New York, N.Y.)》2008,321(5895):1457-1461
Thermoelectric materials are solid-state energy converters whose combination of thermal, electrical, and semiconducting properties allows them to be used to convert waste heat into electricity or electrical power directly into cooling and heating. These materials can be competitive with fluid-based systems, such as two-phase air-conditioning compressors or heat pumps, or used in smaller-scale applications such as in automobile seats, night-vision systems, and electrical-enclosure cooling. More widespread use of thermoelectrics requires not only improving the intrinsic energy-conversion efficiency of the materials but also implementing recent advancements in system architecture. These principles are illustrated with several proven and potential applications of thermoelectrics. 相似文献
8.
猪体细胞克隆胚胎的体外生产试验 总被引：3，自引：0，他引：3
【目的】通过优化猪体细胞核移植程序,建立获得克隆囊胚的有效方法。【方法】比较不同电激活参数、不同体外培养条件对猪体细胞克隆胚发育能力的影响。【结果】选用1.5 kV?cm-1、80 μs 和1 DC的参数组合,对猪核移植重构胚进行电融合和电激活,可获得较高的卵裂率和最高的囊胚发育率（分别为71.4%和14.3%）,且囊胚发育率显著高于其它组（P＜0.05）;0.4% BSA NCSU 23 培养液培养克隆重构胚72 h,半量换液并未改善克隆胚的发育,但添加10% FBS 可显著提高囊胚发育率（15.1%对10.3%,P＜0.05）和DNA 完整率(56.8%对46.6%,P＜0.05) ;采用猪卵泡颗粒细胞（pGC）共培养体系未能显著提高克隆胚发育率（P＞0.05）,但卵丘细胞（pCC）单层共培养时,囊胚发育率显著高于对照组（16.7%对9.8%,P＜0.05）,培养5 d 的克隆胚凋亡率也显著低于对照组（39.5%对54.2%,P＜0.05）。【结论】采用1.5 kV?cm-1、80 μs 和1 DC 的参数组合对猪克隆重构胚进行电融合和电激活,以0.4% BSA NCSU 23培养液作 pCC 单层共培养72 h,然后换用10% FBS NCSU 23 培养液,可明显提高囊胚发育率。 相似文献
9.
Nanoscale architecture was used to control energy transfer in semiconducting polymers embedded in the channels of oriented, hexagonal nanoporous silica. Polarized femtosecond spectroscopies show that excitations migrate unidirectionally from aggregated, randomly oriented polymer segments outside the pores to isolated, aligned polymer chains within the pores. Energy migration along the conjugated polymer backbone occurred more slowly than Forster energy transfer between polymer chains. The different intrachain and interchain energy transfer time scales explain the behavior of conjugated polymers in a range of solution environments. The results provide insights for optimizing nanostructured materials for use in optoelectronic devices. 相似文献
10.
Mezzenga R Ruokolainen J Fredrickson GH Kramer EJ Moses D Heeger AJ Ikkala O 《Science (New York, N.Y.)》2003,299(5614):1872-1874
A route for producing semiconducting polymer blends is demonstrated in which a doped pi-conjugated polymer is forced into a three-dimensionally continuous minor phase by the self-assembly of colloidal particles and block copolymers. The resulting cellular morphology can be viewed as a high-internal phase polymeric emulsion. Compared with traditional blending procedures, this process reduces the percolation threshold for electrical conductivity by a factor of 10, increases the conductivity by several orders of magnitude, and simultaneously improves thermal stability. Following this route, new applications can be envisaged for semiconducting polymer blends that require only minimal concentrations of doped pi-conjugated polymer. 相似文献
11.
本文分析了洁霉素在健康马体内的代谢动力学过程。肌肉注射后血清药物浓度——时间曲线符合开放式二室模型。洁霉素的药代动力学参数如下:药物的分布半衰期(t(1/2α))为0.35±0.34小时,生物半衰期(t(1/2)β)) 为8.08±0.73小时,吸收半衰期(t(1/2)k_a) 为0.14±0.03小时,药物在中央室与周边室间分布的转运速率常数 k_(12)为2.229±1.551(h~(-1))与 k_(21)为0.5129±0.1981(h~(-1)),清除率(CLB)为0.1803±0.0808(ml/kg·h),药物从中央室清除的消除速率常数(kel)为0.5784±0.5644(h~(-1))。根据单剂量给药的参数预测了多剂量给药间隔。给药后12小时的稳态最高与最低浓度为9.66(μg/ml)与6.23(μg/ml),积累系数 R 为1.56。本研究确定洁霉素的给药间隔时间为12小时。 相似文献
12.
Carbon nanotubes display either metallic or semiconducting properties. Both large, multiwalled nanotubes (MWNTs), with many concentric carbon shells, and bundles or "ropes" of aligned single-walled nanotubes (SWNTs), are complex composite conductors that incorporate many weakly coupled nanotubes that each have a different electronic structure. Here we demonstrate a simple and reliable method for selectively removing single carbon shells from MWNTs and SWNT ropes to tailor the properties of these composite nanotubes. We can remove shells of MWNTs stepwise and individually characterize the different shells. By choosing among the shells, we can convert a MWNT into either a metallic or a semiconducting conductor, as well as directly address the issue of multiple-shell transport. With SWNT ropes, similar selectivity allows us to generate entire arrays of nanoscale field-effect transistors based solely on the fraction of semiconducting SWNTs. 相似文献
13.
人工湿地氧化还原特征及其与微生物活性相关性 总被引：3，自引：0，他引：3
在水力负荷为800 mm/d的运行条件下,研究了复合垂直流人工湿地中试系统不同功能层面的氧化还原特征、好氧微生物数量、基质的耗氧速率及氧化还原酶类活性的分布特点。结果表明:各功能层面的氧化还原电位、好氧微生物数量、耗氧速率表层最高,并且随着基质深度的增加逐渐降低。除过氧化物酶外,氧化酶活性表现为表层高于中下层;而硝酸盐还原酶、亚硝酸盐还原酶等活性变化趋势则相反。同时,氧化还原电位与基质中细菌、真菌、放线菌的数量、耗氧速率等存在显著正相关关系;氧化还原电位与多酚氧化酶、过氧化氢酶、脱氢酶等氧化酶活性也存在显著正相关,而与下行流池的硝酸盐还原酶、亚硝酸盐还原酶等还原酶类存在显著负相关关系。 相似文献
14.
目的 研究几种代表性商品化除草剂以及植物源除草化合物小檗碱及其类似物对拟南芥根尖细胞氧化还原电位的影响。方法 以靶向线粒体的氧化还原敏感绿色荧光蛋白（Mitochondria targeted redox-sensitive green fluorescent protein, mt-roGFP1）标记的拟南芥转基因植株为材料,采用不同质量浓度的化合物处理不同时间后,测定拟南芥根冠、分生区、过渡区和伸长区的细胞氧化还原电位的变化。结果 经几种商品化除草化合物处理后,拟南芥根部分生区的细胞氧化还原电位最小。从分生区到伸长区氧化还原电位逐渐增大,呈现逐渐被氧化的趋势。其中,光系统II抑制剂(莠去津和环嗪酮)的氧化还原电位变化规律最为明显,说明mt-roGFP1荧光探针能较好地响应光系统II抑制剂。氨基酸生物合成抑制剂草甘膦对拟南芥根尖细胞氧化还原的影响具有明显的剂量-效应关系,随着草甘膦质量浓度增加,氧化还原电位变化量也逐渐增大,呈正相关关系(R2 =0.9956)。小檗碱及其类似物处理后,大多数处理组的拟南芥根尖细胞的氧化还原电位在分生区达到最大还原值,并从分生区开始逐渐被氧化。结论 研究结果可以为应用roGFP荧光探针技术研究除草化合物对根系细胞线粒体的作用机制提供基础。 相似文献
15.
采用艾比湖的1990、2001与2009年3期Landsat TM/ETM+遥感数据资料,运用ENVI4.5和ArcGIS进行制图分析得到了艾比湖区域土地类型转移矩阵,定量研究了艾比湖区域1990～2009年土地利用类型的时空变化特征,并分析了土地类型转入/转出贡献率。结果表明,1990～2009年,艾比湖绿洲分布特征有明显变化,面积也有显著的扩张,在转入和转出过程中,绿洲和未利用地之间的转换最为密切,水体面积在转换矩阵中基本上保持稳定趋势;从转入贡献率看,占优势的为绿洲,而转出贡献率中占优势的是未利用地。 相似文献
16.
Yella A Lee HW Tsao HN Yi C Chandiran AK Nazeeruddin MK Diau EW Yeh CY Zakeeruddin SM Grätzel M 《Science (New York, N.Y.)》2011,334(6056):629-634
The iodide/triiodide redox shuttle has limited the efficiencies accessible in dye-sensitized solar cells. Here, we report mesoscopic solar cells that incorporate a Co((II/III))tris(bipyridyl)-based redox electrolyte in conjunction with a custom synthesized donor-π-bridge-acceptor zinc porphyrin dye as sensitizer (designated YD2-o-C8). The specific molecular design of YD2-o-C8 greatly retards the rate of interfacial back electron transfer from the conduction band of the nanocrystalline titanium dioxide film to the oxidized cobalt mediator, which enables attainment of strikingly high photovoltages approaching 1 volt. Because the YD2-o-C8 porphyrin harvests sunlight across the visible spectrum, large photocurrents are generated. Cosensitization of YD2-o-C8 with another organic dye further enhances the performance of the device, leading to a measured power conversion efficiency of 12.3% under simulated air mass 1.5 global sunlight. 相似文献
17.
Tezcan FA Kaiser JT Mustafi D Walton MY Howard JB Rees DC 《Science (New York, N.Y.)》2005,309(5739):1377-1380
Adenosine triphosphate (ATP) hydrolysis in the nitrogenase complex controls the cycle of association and dissociation between the electron donor adenosine triphosphatase (ATPase) (Fe-protein) and its target catalytic protein (MoFe-protein), driving the reduction of dinitrogen into ammonia. Crystal structures in different nucleotide states have been determined that identify conformational changes in the nitrogenase complex during ATP turnover. These structures reveal distinct and mutually exclusive interaction sites on the MoFe-protein surface that are selectively populated, depending on the Fe-protein nucleotide state. A consequence of these different docking geometries is that the distance between redox cofactors, a critical determinant of the intermolecular electron transfer rate, is coupled to the nucleotide state. More generally, stabilization of distinct docking geometries by different nucleotide states, as seen for nitrogenase, could enable nucleotide hydrolysis to drive the relative motion of protein partners in molecular motors and other systems. 相似文献
18.
该研究根据微波真空干燥过程中木材内部水分和热量的迁移机理,建立了木材微波真空干燥的数学模型,并通过试验对该模型进行了验证。结果表明:木材的微波真空干燥过程可以分为3个阶段,即快速升温加速干燥段（Ⅰ）、恒温恒速干燥段（Ⅱ）和后期升温减速干燥段（Ⅲ）,且恒温恒速干燥段在整个干燥过程中所占的比例较大;该模型能较好地模拟木材在微波真空干燥过程中的温度和含水率的变化规律,其模拟精度较高,模拟值与试验值之间相关系数的平方在0.9以上,且含水率变化规律的模拟精度高于温度变化规律的模拟精度。 相似文献
19.
Olga S. Walsh A. R. Klatt J. B. Solie C. B. Godsey W. R. Raun 《Precision Agriculture》2013,14(3):343-356
Previous studies have shown the importance of soil moisture (SM) in estimating crop yield potential (YP). The sensor based nitrogen (N) rate calculator (SBNRC) developed by Oklahoma State University utilizes the Normalized Difference Vegetation Index (NDVI) and the in-season estimated yield (INSEY) as the estimate of biomass to assess YP and to generate N recommendations based on estimated crop need. The objective was to investigate whether including the SM parameter into SBNRC could help to increase the accuracy of YP prediction and improve N rate recommendations. Two experimental sites (Lahoma and Perkins) in Oklahoma were established in 2006/07 and 2007/08. Wheat spectral reflectance was measured using a GreenSeeker? 505 hand-held optical sensor (N-Tech Industries, Ukiah, CA). Soil–water content measured with matric potential 229-L sensors (Campbell Scientific, Logan, UT) was used to determine volumetric water content and fractional water index. The relationships between NDVI, INSEY and SM indices at planting and sensing at 5, 25, 60 and 75-cm depths versus grain yield (GY) were evaluated. Wheat GY, NDVI at Feekes 5 and soil WC at planting and as sensed at three depths were also analyzed for eight consecutive growing seasons (1999–2006) for Lahoma. Incorporation of SM into NDVI and INSEY calculations resulted in equally good prediction of wheat GY for all site-years. This indicates that NDVI alone was able to account for the lack of SM information and thus lower crop YP. Soil moisture data, especially at the time of sensing at the 5-cm depth could assist in refining winter wheat YP prediction. 相似文献
20.
It is important to study the soluble organic N （SON） extracted during water-logged incubation for evaluating soil Nsupplying capacity. Soil initial SON and mineral N （Nmin）, cumulative soluble organic N and NH4＋-N in leachates during water-logged incubation, mineralization potentials of both easily decomposable N （ND） and resistant N （NR）, and their relationships with N uptake by crop in pot experiment were investigated by using 10 kinds of farmland soils with widely different physical and chemical properties on the Loess Plateau, China, and the effects of SON on evaluating soil Nsupplying capacity were studied. The results showed that the average content of initial SON （23.9 mg kg^-1） of 10 soils was 28.8% of initial total soluble N and 2.4% of soil total N. The percentage of cumulative SON in leaching total soluble N （118.1 mg kg^-1 was 46.4%, higher than the percentage of initial SON （28.8%）, and almost close to the percentage of cumulative NH4^＋-N in the leachates. ND had close correlation with total N, and the correlation coefficients were 0.92 （P 〈 0.01, excluding SON in estimating ND） and 0.88 （P 〈 0.01, including SON in estimating ND）, respectively. N mineralization potential and mineralization rate constant were different with the soil types. ND of Los-Orthic Entisols and Ust-Sandiic Entisols were lower than that of Eum-Orthrosols. Mineralization rate constant for the fast decomposable N-fraction （kD） decreased and the mineralization rate constant of resistant materials （kR） increased when SON was taken into account. Cumulative NH4^＋-N was a better evaluation index of soil N-supplying capacity, and it is not only suitable for the first season crops but also for two successive season crops. Cumulative SON alone was not a satisfactory index for the potential of mineralizable N. But it would be more accurate for ND in revealing the potential mineralizable N when SON was taken into account. Cumulative TSN, to some extent, could also be taken as an index for 相似文献